Direct-current insertion



Filed July 17, 1940 2 Sheets-Sheet 2 INVENTOR HALLAN E. 60%0 ATTORNEY wmmRGqSw SR L. v MN r v I r v M I '1 m w; 7 N W R. P. Q 3 mT w ,osciilator the frequency of which is modulated Patented Sept. 29, 1942 i azs'ssis Hallan primer-CURRENT nissn'rron 1 E. coldstme, Rocky PointfN. Y., assignor to Radio Corporation of America, a corporation.

of Delaware f Application July. 17, 1940, San; v ialnsas 16 Claims. (01. 178'l.l)

This application concerns frequency modulation of carrier waves in accordance withcontroiling potentials such as, for example, video signals,'andincludes a new and improvedmethod mstmtmg the n t o of y improved method and means; while r Fig.3 illustrates acircuit arrangement of an by video signals in combination with means for inserting a direct-currentpomponent the Q due to, synchr nizing modulator; circuits "to h old the peak deviations impulsesin the assignedposition in thefrequenc'y channel; P

s InFig. 2, I haveillustrated graphically a teleof and means for'providinga direct-current or 5 V slowly'varying bias on the-modulator suchthat Flg,.2a, 'is illustrated graphically the position or peak frequency'deviations will be stabilized in "a;wave, modulatedin frequency by the'televi's'ion' the frequency spectrum regardless of the make: signal and synchronizing, signal, in the "hand-- up or weight or contrast of the subject or picture pass characteristic .of' the system." vIt is noted being sent. r 7 10 that as the picture weight orlratiofloffblaclr to" "Many advantages are to be gained by the 'use whitethereof changes; the mean or carrier freof-frequency modulation television picturetrans- 'quency'C changes'its. position. This resultsfin" mission. In' television pictures 9 the average thatthe peaks P of the deviation'caused by the weight of the picture varies from :time to time synchronizing imp'ulse move to an improper 130- and this resultsinshiiting of themean carrier sitionin the bandpass resulting in distortion. 4 freqiiencywwherf this happens. the peaks of An object 'of 'this'invention is to hold the syndeviations due synchronizing impulses will chronizing peak'gd via i n i t r E d'DO- not fall in the proper positionin v-the'frequency sition in the bandpass of the Y .8 1 spectrum. By using my direct-current insertion trated in Fig. 2b. I method and means peak-frequency deviations Myu'me o M m i ve Shiftinc the due to the synchronizing impulses will be posicarrier or mean frequency as a iunction of the tioned in the same-place in the bandpasscharacpeaks o t e evia on Cause W y r teristic regardless of the nature ,of the picture. nizing impulses so that t e. saidpeak frequency- If mymethod of direct -current insertionis not dfi i' he fi l' r ,T t used, the frequency groupqof the synchronizing 2s and means is'not to 'be'cqnfused with automatic impulses will change-their position in the frefreq encyv lcq trol methodsfand means 'used'in quency spectrum depending upon the} nature of 'fregu'ency modulation systems. In the latter.

, the picture due to-the fact that, in this case;'the1 systems; the mean or carrier frequency is o average en'ergydetermines the effective center trolled as a function of deviations of them an of carrier position. By using my direct-current 30..o r carrier frequency. Q f "f f, insertion method and keeping the peak devise 'Ifhere are several wfays this direct-current intions caused by synchronizing pulses at the same 7 sertion can be applied to a frequency'modula'ted v position withre'spect "to frequency, the synchrotransmitter, and I have; in this applicationpdis- 'nizing impulses will then always be located. in closed-in Fig. l a frequencymodulatedftransmit- 'the'same place-in the bandpass frequencychar 36 ter including the elements by means of which .acteristics andwill not: suffer distortion when iss'upplied the necessaryj iiirect current: or low the nature of the picture changes. i V irequency componentto change the-mean or;

' In describing my invention reference will be I .carrieffrequnpy as aflfi rjctlon of peak synchro made to the attached drawings wherein V nizlng eurrentsfused for modulating th 'traj'n's- 7 Fig. 1 illustrates schematically the principal 4 mitter frequency 31:0 maintain the peaks of units or elements of an oscill i n generatordeviations causedbythe synchronizing impulses modulated as to frequency by signals such as, essentiallyat the sam'e frequency. Inthefsys 101" ex p i i n nalaiin combination tem disclosed; modulation of the carrier fre-' with means arran ed in accordance with m :quency, in accordance with picture signals, is'devention for direct-current insertion in the sys- 45 'scribedbut other signals whereinthe same or tem to hold-the peak deviations due to. synchrosimilar problems arise may be used.

nizing impulses at the proper pointfin the translllf represents anoscill tion source the output 'mitted band; 7 of which is supplied to a unit 20 comprising ampli- V 1 Figs. 2. 2 b and 26' ar 'sr p es i hers and frequency multipliers and limiters or one or more or the'same-as" desired. is a means forj modulating the frequency of the generated oscillations.- This means mamas indicated, comprise a reactance tube modulator. "is a source of modulating potentials indicated here as video signals in anamplifying and limiting. stage.- Thevision a signal] with synchronizing, pulses. --In;

oscillations at III are modulated in frequency by the means 30 under control of the signals from 40 and the modulated oscillations are amplified in 20 and radiated or used otherwise.

7 The'video signals impressed on 40 are therein passed'by an amplifier and, if desired, a limiting plished by impressing the video signals through a condenser on the grids l8 and I8 in phase.

The modulated output is supplied to the grids jof multiplier and/or amplifier and/or limiter amplifiens'o thatthesynohronizing impulses will not change their relative height or amplitudedur ing the program transmission. Frequency modulated carrier wave energy at the oscillator output: u 'or from a multiplier or from the radiating means is picked up and supplied to a sloping "filter and peak detector The sloping. filter maylbe' of the concentric line type,- as described ,inimy United Statesapplication Serial No. 341,111 filed June 18, 1940. If necessary, a limiter 50 may be included between the pickup means'ahd-the" filter 60,

T e-ou t from th fled voltage from thejpeakdetectorlll is passed throughra timeiconstant, circuit and thence to s direct-current ampIifie'rj BOwhereinit is ampli-'-* sloping fll ter may be used .tocontrol a peak voltmeter of the diode or other type sothat the synchronizing pulses will operate a voltmeter on their' peak'amplitude. The recti fied'andapplied to, themodulating means which changes the frequency of the transmitter;

The-necessary time constant ci'rcuits'are includedin the amplifier so that .theflchangein frequency will'be slow and will not present any flicker in the picture background;

InIFig. 3, 1 have illustrated essential details of a ec a l cuency deviations v ,to amplitude changes.

resistancelizand condenser 64 forms a time constages in 20 and; thence, to a utilization means. Some of the modulated wave is fed to a limiter 50 and thence to a resonant circuit, in the form of alineandfrom the line "to the cathode 54 of adiode peak detector 55 the anode of which is ;.connected to ground by a resistance 82. The resonant circuit has a sloping characteristic as illustrated at -C in Fig. 2c and converts the fre- The stant devicewhich passes only the very low alternating current or the direct current.

"Ifhe'peak diode detector may operate at any particular frequency along the line of multipliers. Iri this particular case, I have shown the diode. peak detector coupled to the. 500 Mo. output stage; The diode detector, .is' so biased by resistance .52 and condenser that peak swingsonly-of thewave. due tothe synchroniz} ing impulses'which exceed: a preselectedvalue in the 'frequencyfirahge are operative to produce direct-current output which flows in: the resistance' BZto produce or: the grid- 1| a potential which becomes. more. negative as the current in the rectifier output increases. The diode peak the frequency modulation system of my invention.

v Here, lis an oscillatortub having its anode [and 3 I grid l an'd cathode 8 connected in regenerative circuits.- llfc oupled by condensers BC to the anodes I4 and 14' respectively of the reactance tube modulators l6 and I6. Thegrids l8 and l 8' of tubes I and I condensersjland 22'. to the anodes l6 and 15' re spectively. The cathodes 2 l and 2] are connected {b co'ndensers Hand 23 to ground as is a point ,ontheinductance l3 o'fcircuit It Voltages of the generated-frequency are setup in phase quad- -rature-relation on the grids and anodesofeach tube J4 and Ill so that thesetubes form a variable ,reactance in shunt to the circuits I2. The tubes I 4 and H are shown'in separate envelopes but maybe ina single envelope as for example, a type 832tube may be used. A voltage of the oscillator;

frequency is developed between the anodes I6' and Hi due. to. the radio-frequency in circuit 1 2; The -voltage ,on,the control j'grids l8 and la'jis' advanced scmetmngnke ,90jdegrees by "the condensers 22 and 22? and resistance R.. As a conseage they act like condensers. When the negative bias on. the grids l8andj I8" ofthe-tube's Hand H'is decreased, i. e., when thergridsbecon'ie more positive'due .to modulationvoltages, the current pulses increase in amplitude, the capacityieactance of the reactance tubes due to, electron curcreases and the frequency. of. operation is raised.- "Frequency modulation of theagenerated. oscillations in accordance with video signals is accomdetector" feeds the: grid .1 I; of a direct-current amplifier tube 13 which reverses the phase of the direct current. The anode 15 of the direct-current amplifier liisconnected to, its-cathode by a resistance .liand to the grids l8 and ll of the I reactance tubes I 4- and ll, by the. resistance 18.". "As stated, tube :13,-reverses the-directcurrent so-nthatwhen :the peaks orthe synchronizing pulses" increase current.--.through-resistance 62 increases and the potential supplied-to grid ll becomes more negative; This decreases the cur.- rent output-of. tube 13 ;to:raise the voltageat 7 the plate end of resistance: "16 thus -making the quence, the pulses of current which reachf'each Y anode leadsthe voltage on the saidfanode by about, 90 degrees. Since the reactance tubes here 1 have a plate current w hich'leads t'heplate volt u may be used;

grids lilfand PHI. of i the ,reactance modulator tubes more positive with respect .to the cathodes and thusxcausingwth'e'mean frequency of'operation to decrease. As ;the peaks of frequency swings decrease, the operation; is reversed and this te'rlds' to 'maintainflthe; P691 01 the-wave 5 .swings due to the synchronizing-voltage at about 0,

the/same frequency.

' -The 'dio'deypeak detector in the circuitsshown is associated with a section-of concentrictrans- ,rnission line approximatelya /4 wave lengthlong havinga characteristicasishown at-C inFig. 20. However, :a paralleltuned circuit may be substituted or the sloping, side of a high pass filter What isclaimed isz 1. In a system for controlling the peak-frequencyiswlng's of oscillations, modulated in fre- 'quenc'y by video signals including synchronizing rentdecreases, and the capacitiveeffect reflected in the generator circuits 11 increases thereb'y'jlow- :ering the frequency of operationof the generator.

. Conversely, if the grids l8 and I8, go more negative-the-reactance isincreased, the capacitive efiectrefiected in the generator circuits I 2 deimpulses-irrespective of changes in theaverage weight of said videosignals, means comprising'Ia circuit converting frequency changes to .amplltude changes and a biased rectiflerproducing rectified current only in response to converted waves having excessive peak amplitudes, re-

sponsive to peak frequency swings which go' beyonda selected frequency and meanscontrolled by said lastnamed means for; changing the mean frequencyof said oscillations 'as' a function I of the extent to which saidpeak swings go beyond said selected frequency tothereby maintain the peaks'of ,thesjwings at about said selected frequency.

2., In ,a system for maintaining the maximum frequency of oscillations supplied by" a generator and modulated in frequency by video signjalsincluding synchronizing" signals; at a selected jsubv I stantially fixed frequency irrespective of changes in average weightjof said, video'signals, lrneans' excited by said modulated oscillations and re'-.

sponsiveto peak frequency swings which exceed said selected frequency for producing a'dire'ctcurrent component the intensity of yvhichisa function of theextent of thepeak swings, be yond. said selected frequency said means"com-" prising a biased diode rectifier, and means ex-" cited by said direct v current component for changing-the mean frequency of operation @of said generator as a function of theintensity of said direct-current component."

3.;In a system for maintaining peakjdeviae tionsqof oscillations produced ina generatorjand modulatedin frequency by videosignals includingsynchronizing signals, at a selected substan llv. fi d point in t e r en sp t respective 1 of changes in average weight of said video signals, means comprising'al biased rectifier; having a low time .constant 'outpntfciiflc it. responsive to peak deviations whichlexceed. said;

selected frequency for producing .a "directrcurrent component characteristicof said peak deviations, and means for decreasing the mean fre quency ofoperation of said generator as a function of the intensity of said direct-current component; a

n 4, Apparatus, for limiting thepeak frequency deviations of oscillations modulated in frequency by voltages characteristic of: television'l signals generator at a predetermined point 'i condenser in shunt to said resistor, and/means forw additionaliy' controlling "the impedance of said reactance V tubein accordance withsaid def rived potential.

'I. a frequency modulatormending cs cillation' generator, a reactance- -tube fmo'dulator coupled theretoand means} forcontrolling the impedance of said reactance' "tube by video sig-j ,na'ls, means for deriving from saidmodulated oscillations a. ,direct- 'current' potenti" tional 'to peak swings; thereof "which exceed alected frequency, means'for-rever'fsijng' the a polarity of said direct-currentpotential, and means" for additionally controlling the-fimpedance of said reactance p tube in accordance withtential'of reversed'polarltyi {iIInr'neans to be usedwith an o illationgenerator modulated by video signals for main? taining the" peak deviations of said" quency spectrum irrespective ofchanges'i v trast'of the subiectrepresented byfsaii. deo' signals','fa' reactance tube modulator said oscillation generator" tocoritrol =1 l frequency of operation thereofja cir'cuit having a'sloplng characteristic coupled to' said foscil-j, lation generator,a wave' peak rectifier subjected to an initial bias coupled to-said last named circuitgt o' rectify the" peak 'currents f suppliedi thereby and to derive frjom' summarises-eurwithout disturbing the effector a changefin contrast in said picture on the modulation of said oscillations which includes a, direct current-bivoltage as modified by said time constant circult.

5. Signalling apparatus including a modulator for modulating the frequency of oscillations in accordance with signalling voltages characteristic of a subject and synchronizing voltages, a limiter for limiting the frequency modulated oscillations, a circuit for converting frequency swings of the limited oscillations which-go beyond a selected maximum frequency swing, into corresponding amplitude variations. a biased direct current rectifier for rectifying peaks of amplitude variations to derive a direct current component, and means for controlling the mean frequency of said oscillations in accordance with the amplitude of said direct current component.

6. In a frequency modulator including an oscoupled thereto. and means for controlling the impedance of said reactance tube by signals, meari's' for limiting the modulated waves, means for deriving from said limited modulated oscillations a potential proportional to peak swings thereof which go beyond a selected frequency 7 said last-mentioned means for deriving said potential comprising a diode detector, a'resistor connected in series with the cathode of said derents e i ect-current potential, and a coupli gbetween said 'wave peakrectifier and" anelectrode ings'a'id' reactancetube-to f control the 1mg .pedancethereofsaid couplingzincluding an'elecf I r char de i e,- i

means tobeusedwith an oscillationg'en erator' modulated by video signals for maintaining' the peak deviations-"of "said-oscillation generator at a predetermined point" in the "ire quency spectrum irrespective of changes in ;average intensity offthe said video signals; a'' re a'ctance tube modulator couplditvitlfsaidjos cillation 1 generator to control in part the E frequency of operation thereof, a circuit avings sloping characteristic coupled t'o- 'said oscillaf t'lon generator, a wave peak "rectifier" coupled to'said last named circuit-"to'rectifyrthe peak currents supplied thereby and to derive from said rectified'currents a direct-current potential, a direct-current potential amplifying and reversing tube having input electrodes coupled to said rectifier and. a coupling between the output electrodes of said amplifier tube and an elecfor producing current when said selected frequency is exceeded, said rectifier comprising a biased diode, and a controlcircuit coupled to 'said diode rectifier and controlled by said ourcillation generator, 8. reactance tube modulator 10. In a system for maintaining the, peak frequency swings of oscillations modulated in fre- I quency by signals, at a selected substantially fixed frequency irrespective; of changes in the average intensity of said signals, acircuit including a peak rectifier responsive to frequency swings which go beyond said selected frequency rents for changing the mean frequency of said oscillator as a function of the extent'to which sad peak swings go beyond saidselected frequency to thereby maintain the, peaks of the swings at about said selected frequency.

vl1. In a system for maintaining peak deviations of oscillations produced "in a generator and modulatediin frequency by video signals tector so as to cause self-biasing thereof, and a rirojrrirscillat A n.

r including synchronizing signals-at a selectedsubstantialiy fixed point in the frequency spectrum' irrespective of changes in theaverage. weight of said video signals, a limiter for limiting the modulated oscillations, a circuit comprising a di-' rect current biased detectcr'fon producing from the limited oscillations, a. direct current .com-

ponent characteristic of peak deviations of said tential proportional to the peak swings thereof which exceed a selected frequency, an electron discharge tube coupled to said rectifier for I reversing the polarity'ofsaid" direct current potentiaL'and a control circuitcoupled to said last tube and to said reactance tube for additionally contrclling'the impedance ofsaid reactancetube oscillations which exceed said selected frequency, v

and a control circuit coupled to said' last named circuit and responsive to said. direct currentcomponent for controlling the means frequency of operation of said generator..

12. In a 'frequency'modulator including an oscillation generatona reactance tube modulator in accordance with said poential of reversed'polarity. r V v 15. In a wave length modulation system, a circuit wherein wave energy the wave length of "which is to be modulated fiows, a modulation circuit coupled-to said first named circuit and coupledl'thereto. and means for contr olling the V impedance of saidnreactance tube by video signals, a'frequencyresponsive circuit iand a biased rectifier having a low time constant'outputcir- 'cuit coupled :to said generator for deriving from said modulated oscillations a potential propor-1 tionalflto peak swings thereof which go beyond a selected frequency, and, a; control circuitcou pied tosaidlast named circuit and to vSaid generator for additionally controlling the frequency of the oscillations generated in accordance withsaid derived potentials.

13. In a frequency modulatorincludingan os- 'cillationgenerator, a 'reactance tube modulator coupledtheret'o' and meansforj controlling the impedance of said .reactance tube by video signals a frequency responsivejcijrcuit and a recticontrolled byvideo'signals including synchronizing signals for moduulating the wave length I ;of the oscillations generated insaid circuit, a-

wavelength responsive circuit and a biased wave peak rectifier excited by modulated wave energy derived from said responsive circuit for producing currents characteristic of peak deviations in the wave length'of said wave energy which ex-,

. ceed aselected deviation, and a control circuit 7 coupling said rectifier to said first named circuit for additionally controlling the wave length of fier for deriving fromsaid modulatedoscillations a direct current. potential proportional to" the peak swings thereof which exceed .aseiected frequency, an electron discharge tube for reversing the polarity. of saiddirectcurrent potential, and

acontrol circuit foradditionally controlling the impedance of said reactance tube in accordance with said potential of reversed polarity.

.14. In a frequency modulator including an oscillation generator, a reactance tube modulator coupled thereto and means for controlling the impedance of said reactance. tube byivideo sig-' nals, a:frequency"responsivecircuit and a rectiiiercoupled to said generator-for deriving from saidfmodulatedoscillations a direct current. po-

' said selected frequency for producing current when said selected frequency is exceeded, connections between said circuit and said current amplitude limiter, and a control circuit coupled to said peak rectifier and'controiled by said currents for changing the meanfrequency of said oscillator as a function of the extent to which said peak swings go beyond said selected frequency to thereby maintain'the peaks of the swings at about said selected frequency.

/ E. GOIDSTI'INE. 

